Eddy current preloaded controllable speed motor



Jan. 3, 1950 P. w. WENDELBURG El AL 2,493,607

EDDY CURRENT PRELOADBD CONTROLLABLE SPEED MOTOR 3 Sheets-Sheet 1 Filed Oct. ISO, 1947 Big! 1040 {xxx anions: 7mm? W. [leak/)? z, 5710)! Kiwis/1011121 [Am/1d ,fllarwe r Jan. 3, 1950 F. W. WENDELBURG ET AL EDDY CURRENT PRELOADED CONTROLLABLE SPEED MOTOR Filed Oct. 30, 1947 3 Sheets-Sheet 2 .rfl/arney Jan. 3, 1950 F. w. WENDELBURG ET AL EDDY CURRENT PRFLOADED CONTROLLABLE SPEED MOTOR :5 Sheets-Shet 3 Filed Oct. 30, 1947 fir/927K021: jam? 1/ Mam diary /LM a 7% Patented Jan. 3, 1950 EDDY CURRENT PRELOADED CONTROL- LABLE SPEED MOTOR Frank W. Wendelburg and Erwin C. Brckelbaum, Milwaukee, Wis., assignors to Hamischleger Corporation, Milwaukee, Wis., a corporation of Wisconsin Application October 30, 1947, Serial No. 782,998

12 Claims. 1

This invention relates to speed controlling means for alternating current motors, more particularly to an apparatus adapted to regulate and vary the speed of an induction motor subjected to variable loads including overhauling loads and resides in an apparatus in which an alternating current motor, with means for selectively varying the input thereto, is so coupled with means depending upon eddy-current induced opposing torque that any selected speed of the motor in either direction of rotation will remain comparatively constant regardless of load variation including the imposition of overhauling loads.

In hoists and cranes which impose overhauling loads the use of direct current driving machinery has long been preferred particularly where wide variation in the load to be handled is involved. This preference has been based upon the fact that direct current equipment may be constructed in such a way that the direction of movement of the load and its rate of travel both during lifting and lowering may be forecast by an operator even though the weight of the load be unknown. These desirable properties of direct current equipment are dependent in part on the advantageous characteristics of so-called dynamic braking and in part upon the ease of providing comparatively "flat speed torque characteristics in direct current motors. In the case of alternating current driven hoists and the like dynamic braking is not possible at speeds less than the synchronous speed of the motor. Furthermore, in alternating current equipment the torque exerted by the motor varies markedly with changes in speed with the result that it is difficult to forecast the rate and even direction of movement of loads of unknown weight.

Numerous efforts have been made to provide control systems which may be used in conjunction with alternating current induction motors for the purpose of causing them to respond more nearly in the manner of direct current equipment. Some of these approximate the performance desired to a considerable degree but the apparatus required for the purpose is elaborate and expensive and often requires considerable maintenance.

In accordance with this invention an induction motor is provided with means for selectively varying the input thereto, for example, as by varying the secondary resistance of a wound rotor motor or by adjustment of input voltage or phase relationship in a squirrel cage or wound rotor motor and there is placed in driven relationship with the shaft ofthe motor eddy-current torque-resisting means in which localized areas of magnetic flux are caused to sweep through a magnetic material thus giving rise to eddy-currents which resist the rotation of the motor shaft when excitation current regulated in keeping with the input to the motor is applied. With these elements thus interrelated the net characteristics of the motor when operating with any given input are rendered such that the rate of speed of the motor will remain comparatively constant whether the torque demand be light or heavy. This result follows since the drag of the eddy-current torque resisting means diminishes as motor speed diminishes and increases as motor speed increases which properties are the inverse of the speed 15 torque properties of the motor itself. The same or a similar result follows but at different speeds when different inputs to the motor and different degrees of excitation of the eddy-current torque resisting means are applied and also when the motor is reversed and the apparatus is employed for lowering a load.

The manner in which the above results and advantages of this invention are obtained will become apparent from the description following which is set forth by way of illustration and not of limitation reference being had to the accompanying drawings which form a part hereof.

In the drawings:

Fig. 1 is a circuit diagram of one form of the apparatus of this invention;

Fig. 2 is a circuit diagram of another form of the apparatus of this invention;

Fig. 3 is a side view partly in section of an eddy-current torque resisting means mechanically connected with the shaft of a motor in accordance with this invention; and

Fig. 4 is a fragmentary detail end view partly broken away of the eddy-current torque resisting means shown in Fig. 3.

In the form of apparatus of this invention diagrammatically shown in Fig. l a wound rotor induction motor I of conventional form is employed. Mechanically connected to the shaft 2 of motor i and to the right of the same is a generator 3 the purpose of which will be more fully described hereinafter. On a further extension of the shaft 2 and to the right of generator 3' there is mounted an eddy-current torque resisting means or brake 4 having an exciting winding 5. The manner of functioning and the construction of the eddy-current torque-resisting means 4 will be described more in detail hereinafter.

The shaft 2 of the motor I extends also to as the left and is engaged by a mechanical brake agoo? 8 adapted to be released by the supplying of current to a magnet winding I. The brake I is of conventional construction such as is commonly employed for the stopping and holding of motors when power is not being supplied thereto and is, therefore, not described in detail herein. To the right of the motor I there is diagrammatically indicated a hoisting drum 8 upon which a line sustaining a load is wound.

Connected to the secondary of motor 2 by leads 8. III and II are external resistance grids l2, I8 and I4 which are tapped in conventional manner with leads from said taps being extended to fingers of a conventional drum type controller contained within the rectangle I5.

Power for the operation of the motor I is supplied from a source I6, I! and I8 which extends through a disconnect switch I8 to the terminals of a hoisting contactor and in similar manner to the terminals of a lowering contactor 2|. For causing the hoisting contactor to be closed a winding 22 is provided which is connected on the one hand through lead 23, limit switch 24 and lead 25 with the source lead I6. On the other hand, the winding 22 of contactor 20 is connected through a lead 26 with a finger 21 of the controller I5. When the controller I5 is moved to the first hoisting position finger 21 engages segment 28 which through connection with segment 28 joins finger 21 electrically to finger 30. Finger 30 is connected in turn through lead 3I with normally open contact 32 of current relay 33. Under normal conditions for reasons which will be later explained contact 32 will be found closed and the circuit therefor extends thence through leads 34 and 35 back to the source lead I8.

Whenever disconnecting switch I8 is closed, power is supplied through leads Hand 31 to a transformer 38 which supplies current to a fullwave dry-disc rectifier 39. The output of the rectifier 39 is carried by lead 40 on the one hand to one terminal of the winding 5 of the eddycurrent torque resisting means 4. Th output of the rectifier 39 is carried on the other hand through lead M to coil 42 of current relay 33. The opposite terminal of coil 42 is connected by a lead 43 with a normally closed contact 44 of a power failure relay 45. From contact 44 the output of the rectifier 39 is extended by a lead 48 to finger 41 of controller I5. With the controller I5 in the previously described first hoisting position, segments 48 and 49 join lead 46 through finger 50 to lead 5| which is connected in turn through lead 52, resistor 53 and lead 54 with the opposite side of winding 5 of the eddy-current brake 4 producing maximum excitation thereof.

With the controller I5 in the off position as shown in Fig. 1 lead 46 is connected to segment 48 and thence to segment 55. Finger 56 also remains in contact with segment 5-5 and the latter is joined by lead 51 and resistor 58 with lead 54 causing a moderated current to flow in winding 5 of eddy-current brake 4. This current and the augmented current which results by movement of the controller to the first hoist position both are sufficient to excite winding 42 to the point where current relay 33 moves to the position opposite that shown in Fig. 1. Closing of th disconnect switch I9, therefore, places the apparatus in condition where movement of the controller into any of the hoist positions immediately energizes coil 22 in the hoist contactor 20.

Movement of the controller I5 into the first hoist position also brings segments 58, 58 and II into contact respectively with fingers 82, 83 and 54 thus closing the secondary resistor grids I2, I3 and I4 through leads 65, and 81 in such manner as to complete the secondary circuit of motor I with substantial resistance contained therein. Motor I under these conditions will accelerate in a forward direction causing the load to b raised. Speed increases until the torque output of motor I falls to the point where it is equal to the torque imposed by the load plus the resisting torque imposed by the eddy-current torque resisting means 4. Thereafter the load will continue to raise at a steady speed. If the load be heavy, the steady speed attained will be somewhat lower than that attained if the load be light. However, due to the properties of the eddy-current resisting means 4 this difference has been found to be not to exceed mor than a small fraction of the full rated speed of motor I.

By movement of the controller I 5 into the succeeding hoisting positions indicated, the secondary resistance of motor I is progressively diminished through engagement of segments 68, 59, III and II with fingers I2, I3, I4 and 1-5 which are Joined in turn through leads I8, 11, I8 and 19 with the grids I2, I3 and I4 as shown.

As succeeding hoisting positions are racked up on the controller excitation of winding 5 of eddycurrent resisting means 4 are accordingly modifled. For example, in hoisting position 3 the output of rectifier 39 becomes supplied through lead 51 and resistance 58 thus reducing the excitation of'winding 5 and imposing a somewhat smaller opposing torque on the motor I, thus giving rise to an increased hoisting speed even though the secondary resistance of motor I remains unchanged.

In the fourth position of controller I5 excitation current supplied to eddy-current resisting means 4 is dependent upon contact of the segment 88 with finger 8| which joins through lead 82 with resistance 83 thus further reducing the excitation furnished to the winding 5 of the eddycurrent resistance means 4.

In all hoisting positions of controller I5 beyond the fourth hoisting position, excitation of the winding 5 of eddy-current resisting means 4 is terminated. When this occurs current relay 33 returns to the position shown in Fig. 1 thus interrupting the circuit upon which maintenance of the winding 22 of hoisting contactor 20 has heretofore been dependent. Under these circumstances, however, controller segment 84 comes in contact with finger 85 and thus through lead 88 maintains contact with lead 35 and supply lead I8.

When lowering of the load is required assuming controller I5 to be in the off position shown, motor I is stationary, brake 6 is set and power is cut oil the motor I. Winding 5 of eddy-current resisting means 4, however, is excited moderately as heretofore described by reason of the segments 48 and 55 which remain continuously in contact with fingers 41 and 58 when the controller is in off position. Movement of the controller to the first lowering position brings segment 81 in contact with finger 50 thus furnishing maximum excitation current to the eddy-current resisting means. At the same time segments 88 and 89 through engagement with fingers 90 and 30 complete a circuit from supply lead I8 through leads 35 and 34, contact 32, lead 3I, finger 30, finger 88 and lead 9| with winding 82 of hoisting contactor 20. Hoisting contactor winding 82 is connected in turn through lead 83 with In succeeding lowering positions of controller I through engagement of segments 04, 95, 36, 31, 98, 99, I00, IM and I02 with corresponding controller fingers including fingers I03 and I04 not heretofore described causes motor I to apply reverse torque, that is to say, torque in the same direction as thatexerted by the load in varying amount in addition to the torque imposed by the load; thus making available increased lowering speeds on this account.

In addition upon reaching lowering position I excitation of winding 5 of eddy-current resisting means 4 becomes diminished by reason of disengagement of segment 81 from finger 50 and in lowering position 8 excitation of winding 5 is terminated by reason of disengagement of seg ments 48 and 55 from fingers 41 and 56. At the same time segment I05 comes into'contact with finger 85 to preserve current in winding 92 of lowering contactor 2I upon the opening of current relay 33.

During lowering, augmented reverse torque due to a heavy load becomes offset by a slight increase of speed causing the resisting torque of the eddycurrent torque resisting means 4 to increase accordingly. In any position of the controller during lowering, increase of speed produced by increasing the load from zero to maximum load produces a change not exceeding a small fraction of full rated speed under no load conditions of motor I.

Inasmuch as control of the lowering of the load with the apparatus of this invention is accomplished without resort to the use of plugging counter-torque, exerted by motor I, there is no danger that a light load may be lifted instead of lowered by movement of the controller into any lowering position. Lowering of an empty hook or a very light load'is, therefore, positive. Also by reason of continuous excitation of the torque resisting means 4 in the off position, momentary jerking of the load is avoided upon racking of the controller I5 to and from off position before or after either hoisting or lowering.

In order to overcome the difiiculty which might arise through power failure with brake 6 defective or other mechanical derangement such as a broken motor shaft existing and with a load in hoisted position, generator 3 previously referred to is provided. Generator 3 is self excited and thus unaffected by power failure and is connected on the one hand through lead I06 with winding 5 of eddy-current torque resisting means 4 and on the other hand through lead I01 and I98 with the normally closed contact I09 of current relay 33. With no power available rectifier 39 will have no output and the contact I09 above referred to will be in closed position as shown in Fig. 1. Continuing from contact I09 through lead H0 and normally closed lock-out contact III, lead H2 and normally closed lock-out contact II3 generator 3 is joined by lead II4 to winding II6 of power failure relay 45. Winding III; is connected in turn through lead II1 to lead 40 and thence to the opposite side of generator 3.

Power failure alone normally cannot give rise to a hazardous condition since brake 6 when in good condition will hold whatever load has been 6 hoisted. However, since brake 0 is a friction device and may become worn or failure of some other mechanical part may occur and this condition may not be discovered until power failure occurs, a hazardous condition could result which might cause a precipitate descent of the load. This condition, however, will not occur with the apparatus of this invention since acceleration of motor I by the descending load will cause generator 3 acting through the circuit above described to cause closing of power failure relay 45 thus establishing a circuit from generator 3 through lead I01, lead II8, contact II9, lead I20 to lead 52 and thence through resistance 53 and lead 54 to the winding 5 of the eddy-current resisting means 4, which is connected as already described through lead I06 to the opposite side of generator 3. Excitation current is thus supplied in amount sufficient to cause a very slow descent of the load even though it be very heavy.

This emergency restraint will go into operation regardless of the position of the controller I5. That is to say, the automatic restraint will become operative when the controller is in any of the hoisting or lowering positions as well as in the off position. This is in contrast with the properties of the usual direct current dynamicbraking type of hoist control in which emergency restraint of lowering, in case of power, failure, coincident with a mechanical derangement, depends upon maintenance of the controller in either the off position or in'one of the lowering positions. If a person operating such a system in the excitement of an emergency places the controller in one of the hoisting positions, disastrous dropping of the load will result. This hazard is avoided in the apparatus of this invention since the power failure relay 45 will close whenever generator 3 is being driven and a power failure occurs causing current relay 33 to open which actions are independent of the position of controller I5.

If desired an accumulator or other standby source of excitation current equivalent to the generator 3 may be substituted for the generator 3. In case an accumulator is used the same may be arranged to be recharged by the rectifier 39.

Where emergency restraint of the type above referred to is not required the generator 3 and relays 33 and 45 may obviously be dispensed with. Also if desired, generator 3 may be retained and rectifier 39 may be dispensed with. Where a generator such as generator 3 is employed as a source of excitation current, better speed regulation by the eddy-current torque resisting means 4 may be obtained because of changes in excitation current caused by'changes in speed of the generator.

In the event a motor of large size is employed, the circuit of this invention may be so constructed that a light drum controller or selector switch may be employed and all load currents may be handled through magnetic contactors. The apparatus of this invention when thus constructed may take the form illustrated in Fig. 2.

As shown in Fig. 2 the apparatus derives its power from a source I2I which is connected through hoist contactor I22 and lowering con tactor I23 with the power leads I24 of the motor I25 in such manner that forward and reverse driving of the motor I25 may be obtained. The secondary of motor I25 is connected through leads I26 with a resistor grid arrangement of conventional form shown enclosed within the dotted rectangle I21. The resistor grid is connected through leads as shown with magnetic contactor switches I28, I29, I30, II and I32, the

latter serving upon being closed to selectively vary the external resistance of the secondary of motor I25.

Mounted upon the shaft I33 of motor I25 are winding I36 of the eddy-current torque resisting means I 35. The output of rectifier I is connected through lead I42 with the normally closed contact I43 of a power failure relay I44 and thence through lead I45 with the coil I46 of current relay I41. From coil I46 lead I48 extends to the normally open contacts of excitation relays I49 and I50 as shown. Through leads II and I52 and through resistances I53 and I54 the circuit is extended through lead I55 to one terminal of winding I36. The opposite terminal of winding I36 is connected through lead I56 and lead I51 back to the rectifier I. In this way excitation current is furnished to the winding I36 upon closure of either excitation relay I49 or I50. Such excitation current is of a smaller value when the contactor I50 only is closed. When the contactor I49 is closed excitation current is increased by reason of reduced resistance in the circuit.

For the purpose of controlling the opening and closing of excitation relays I49 and I50 and for selection of predetermined resistances in grid I21, a drum controller I58 is provided. When controller I58 is moved to the first hoist position, engagement of segment I59 with finger I60 establishes connection between the winding of excitation relay I50, through lead I6I with segment I62 and thence through finger I63 and lead I64 with adirect connection to power source I2I. The opposite side of the winding of excitation relay I50 is connected through lead I65 also with current source I2I causing relay I50 to close thus establishing current in the winding of current relay I41.

At the same time engagement of segment I80 with finger I8I causes closure of excitation relay I49 by reason of lead I82 which is connected therewith. This causes closure of normally open contact I66 of current relay I41 thus providing a path through leads I61, I68, finger I69, segment I10, segment "I, finger I12 and lead I13 to the winding of hoist contactor I22. The winding of hoist contactor I22 is connected in turn through lead I14, limit switch I15 and lead I16 to the current source I2I thus causing hoist contactor I22 to close. At the same time segment I11 by engaging finger I18 completes a current path through the winding of resistance contactor I29 which passes from the current source I2I through lead I 65 and thence from the winding of contactor I29 through lead I19 to the finger I18. From the finger I 18 the circuit passes through segment I11, segment I10, finger I69, lead I68, contact I66 and lead I61 back to the current source I2I.

There is thus established a pre-determined resistance in the secondary of motor I25 and a pre-determined excitation of eddy current torque resisting means I35 and the motor I25 moves in a hoisting direction.

Upon movement of controller I58 to the second hoisting position segment I disengages from finger I8I thus interrupting current to the winding of excitation relay I49 reducing the current in the eddy-current torque resisting means I35. This permits motor I25 to operate at increased speed. At the same time segment I83 engages finger I84 thus completing a circuit extending from the current source I2I to the contact I66 and leads previously described to the lead I85 and lock-in contact I86 of resistance contactor I29 to lead I81 which joins with the coil of resistance contactor I30 causing the same to close. In this way secondary resistance of motor I25 is further reduced contributing also to increased speed of motor I25.-

In the third hoisting position of controller I58 segment I59 leaves the finger I60 thus de-energizing the eddy-current torque resisting means I35. At the same time segment I83 leaves the finger I84 causing resistance contactor I30 to open. With the complete absence of resisting torque on the part of eddy-current torque resisting means I35, motor I25 increases its speed even though secondary resistance is somewhat diminished.

In the fourth hoisting position of controller I58 segment I88 engages finger I84 and, all other conditions remaining constant, closure of resistance contactor I30 again takes place causing further increase in speed of motor I25.

In the fifth hoisting position of controller I58 segment I89 comes in contact with finger I90 and segment I9I comes in contact with finger I92. As a result resistance contactors I 3| and I 32 are closed reducing secondary resistance in motor I25 to a minimum to cause the motor to operate at maximum speed.

When controller I58 is moved in the lowering direction, into its first position. segments I93 and I94 by engagement with fingers I60 and I8I cause maximum excitation of the eddy-current torque resisting means I35. At the same time engagement of segment I95 with finger I69 and segment I11 with finger I96 completes a circuit through lead I91 and through the winding of lowering contactor I23 which is joined with the current source I2I through lead I65. Power for release of brake I31 is thus furnished but by reason of the open condition of the secondary circuit of motor I25 no torque is exerted thereby and lowering of the load is entirely under control of the eddy-current torque resisting means I 35.

Movement of controller I58 into the second lowering position brings segment "I into contact with finger I98 thus causing resistance contactor I28 to close and causing motor I 25 to exert a small amount of torque to augment that contributed by the load and thus to overcome the torque resisting means I35 at a higher rate of speed.

Movement of controller I58 into the third lowering position brings segment I9I into contact with finger I84 causing resistance contactor I30 to close thus further augmenting the reverse torque of motor I25 causing an increased lowering speed.

Movement of the controller I 58 into the fourth lowering position causes the segment I94 to leave the finger I8I and brings the segment I99 into contact with finger I92. Thus excitation of the eddy-current torque resisting means I35 is diminished and secondary resistance of the motor I25 diminished through closure of resistance con- 9 tactor I3I. An increased rate of loweringspeed, therefore, results.

Movement of controller I53 into the fifth lowering position causes segment I93 to leave the finger I50 thus discontinuing excitation of the eddy-current torque resisting means I35. At the same time segment I10 is brought in contact with finger I30 thus closing resistance contactor I32 and reducing external resistance in the secondary of motor I25 to a minimum. Maximum lowering speed, therefore, results and braking action then becomes dependent upon regenerative braking speeds'in excess of synchronous speed of the motor I25.

During high speed hoisting and lowering under which conditions the eddy-current torque resisting means I35 is not excited, maintenance of the closure of the hoist contactor I22 and the lowering contactor I23 is brought about by engagement respectively of segment 200 with the finger I or the engagement of segment 202 with the finger 20I. I

In the case of power failure under conditions where mechanical brake I31 has been disabled, or other mechanical derangement has occurred, safe lowering will, nevertheless, result by reason of the action of generator I34 which becomes connected to winding I30 through normally open contact 203 of power failure relay I44. Closure of power failure relay I44 occurs whenever hoisting and lowering contactors I22 and I23 are both in open position and current relay I41 is de-energized providing, of course, that generator I34 is being driven. Thus the load is lowered at a safe speed even though power at the source I2I has failed and the brake I31 has suffered damage to the point where it is not capable of holding the load against descent or some other mechanical derangement has occurred.

If desired as in the case of the apparatus shown in Fig. 1 the apparatus shown in Fig. 2 may be so arranged as to maintain excitation of the eddycurrent torque resisting means I35 while the controller I58 is in off position. For this purpose it is necessary only to' merge the controller segments I59 and I 93 so that they remain continuously in engagement with finger 15 and to merge the segments I62 and 200 so that they remain continuously in engagement with finger I63. As explained earlier pre-excitation of eddy-current torque resisting means I35 gives the operator an improved command of the load at the moment when the controller is shifted to and from the off position from either hoisting or lowering positions.

While eddy-current torque resisting means are old and well known and the details of construction of the same form no part of this invention there is set forth in Fig. 3 in simplified diagrammatic form one embodiment of an apparatus of this type suitable for use with this invention.

As shown in Fig. 3 motor 2| 9 is provided corresponding with the motor I in Fig. 1 or the motor I in Fig. 2. Mounted upon the frame of the motor 2I9 is a magnetically released mechanical brake 204 corresponding with the brake 6 in Fig. 1 or the brake I31 in Fig. 2. To the right of motor 2I9 and illustrative of a means imposing an overhauling load is a drum 205 corresponding with the drum 8 in Fig. 1 and the drum I in Fig. 2.

Drum 205 is representative only of a typical load since it is obvious that the motor 2I8 may be connected through gearing or otherwise to any type of load desired.

To the right of drum 205 is a generator 203 the same corresponding with the generator '3 shown inl 'ig. 1 or the generator I34 shown in Fig. 2.

To the right of generator 200 is an eddy-current torque resisting means designated generally by the numeral 201. In the form shown in Fig. 3 and in greater detail in Fig. 4 the torque resisting means 201 is made up of a stationary frame formed of an end plate 208 joined by means of spaced vanes 209 with a stationary field ring 2I0. These parts are preferably integrally joined by welding or by casting in one piece and form the stationary frame of the torque resisting means 201. Extending inwardly from field ring 2I0 is a plurality of spaced magnetic'flngers or poles 2 so shaped as to provide an annular passage within which excitation toroidal winding 2I2 is received.

In the center of stationary end plate 203 is mounted a bearing 2I3 upon which shaft 2I4 is rotatably carried. Secured to the shaft 2I4 to rotate therewith as shown is a hub 2I5 to which there is secured a plurality of circumferentially spaced radially disposed cooling vanes 2"; which merge at their outer limits with a continuous band of magnetic material 2 I 1 within which eddy-' currents are created when relative motion between the band 2I1 and the fingers 2 takes place with excitation current flowing in the winding 2I2. The use of short circuited conductor bars embedded within the band 2I1 tofacilitate formation of eddy currents is not necessary but such may be resorted to if desired. Also secured to the shaft 2I4 to rotate with it is a centrifugal blower assembly 2! adapted to cause a flow of air through the apparatus to dissipate heat which originates therein. The eddy-current torque resisting means 201 corresponds with the equivalent apparatus indicated at 4 in Fig. 1 and at I35 in Fig. 2.

While in the apparatus above described there is a counter-loading of the motor and hence a dissipation of energy in all except the full speed operating conditions of the motor the loss of efficiency occasioned thereby may well be tolerated in view of the improved regulation of speed of the motor.

We are aware that others have heretofore attempted to improve the speed load characteristics of alternating current machinery through torque resisting or dragging means but these have all involved or depended upon mechanical friction devices together with means responsive to motor conditions for regulating the engagement pressures thereof. Such an apparatus suffers the disadvantage of wide fluctuation of friction coefficients due to fluctuation in temperature, degree of wear and the presence or absence of lubrication. Through experience it has been found that friction coeflicients fluctuate so widely that sufficiently dependable speed-torque relationships for successful operation are not obtainable in this way.

With the apparatus of this invention herein disclosed, characteristics are not dependent in any way upon the engagement of frictional parts. Alterations of temperature produce but a minor effect upon the resulting performance with the result that the apparatus of this invention has a consistent response throughout its normal life. There is thus obtained through comparatively simple, reliable and rugged means speed regulation and control of hoisting equipment with the use of alternating current equipment which compares favorably with that obtained with direct current equipment.

We claim: I

l. The combination with an alternating current motor oi means adapted to selectively vary the amount of power delivered'to said motor, eddy-current torque resisting means mechanically connected with the shaft of said motor including windings adapted upon excitation to give rise to eddy-currents which create a field which resists rotation of said motor, a selectively variable excitation current source for said windings adapted to provide independently ofthe speed of said motor a plurality of predetermined different substantially constant excitation currents, and interlocking control means coacting with said means for selectively varying the amount of power delivered to said motor and said selectively variable excitation current source adapted to position the same in predetermined coordinated relationship.

2. The combination with a wound rotor alternating current induction motor of means adapted to selectively vary the external resistance of the secondary of said motor, eddycurrent torque resisting means mechanically connected with the shaft of said motor including windings adapted upon excitation to give rise to eddy-currents creative of a field which resists rotation of said motor, a selectively variable excitation current source for said windings adapted to provide independently of the'speed of said motor a plurality of predetermined different substantially constant excitation currents, and interlocking control means coacting with said means for selectively varying the amount of power delivered to said motor and said selectively variable excitation current source adapted to position the same in predetermined coordinated relationship.

3. The combination comprising a wound rotor alternating current induction motor, external resistance means having a plurality of adjustment taps connected to and adapted to selectively vary the external resistance of the secondary of said motor, eddy-current torque resisting means mechanically connected with the shaft of said motor including windings adapted upon excitation to give rise to eddy-currents which create a field which resists rotation of said motor, means including a tapped resistor adapted to supply excitation current to the windings of said eddycurrent torque resisting means in selectively variable amount, and a controller having a plurality of control positions connected to the taps of said motor external resistance and to the taps oi said excitation resistor adapted to effect a predetermined selection of excitation current for each pre-determined selection of motor external resistance.

4. In an apparatus adapted to lift and lower an overhauling load the combination comprising a wound rotor alternating current induction motor having a shaft, means adapted to connect an overhauling load to said motor shaft, means adapted to selectively vary the external resistance of the secondary of said motor, eddy-current torque resisting means mechanically connected to said shaft including an excitation winding, a source of current adapted to be connected to the winding of said eddy-current torque resisting means to excite the same, a self excited generator mechanically connected to said motor shaft to be driven thereby. and means rendered operative upon failure of said excitation current source adapted upon such failure to connect the output of said generator to the winding of said eddycurrent torque resisting means.

5. In an apparatus adapted to lift and lower 75 an overhauling load the combination comprising a wound rotor alternating current induction motor having a shaft, means adapted to connect an overhauling load to said motor shaft, means adapted to selectively vary the external resistance of the secondary of said motor, eddy-current torque resisting means mechanically connected to said shaft including an excitation winding, a source of current adapted to be connected to said eddy-current torque resisting means to excite the same including means adapted to selectively vary the amount of said current, means adapted to selectively establish simultaneously a pre-determined external resistance for the secondary of said motor and a pre-determined excitation current for said excitation winding of said eddycurrent torque resisting means, a self excited generator mechanically connected to said motor shaft tobe driven thereby, and means rendered operative upon failure of said excitation current source adapted on such failure to connect the output of said generator to the winding of said eddycurrent torque resisting means.

6. In an electrically driven hoist the combination comprising a motor; a hoisting drum connected to said motor to be driven thereby; an .electro-magnetically released brake connected to said motor and drum and adapted to hold the same against movement at all times except when power is delivered to said motor; a source of power for said motor including a controller having a plurality of hoisting and lowering positions and an off position; an emergency load restraining means including an electro-magnetically excitable. eddy current torque resisting means and a source of current independent of said source of power for said motor for exciting the same; and power failure means independent of said controller adapted upon failure of said power source to form a connection between said source of current independent of said source of power and said eddy current torque resisting means to excite the same upon movement of said drum, whereby restraint of a descending load is provided in all positions of said controller whenever failure of said motor power source and said brake occur simultaneously.

7. That form of the combination defined by claim 6 in which the source of current independent of the source of power for said motor comprises a generator mounted to be driven when the drumis in motion.

8. In an alternating current driven hoist an alternating current motor, a source of power for the same, a hoisting drum mounted in driven relationship to said motor, an eddy current torque resisting means connected to said motor to be driven thereby and includinga winding adapted on excitation to give rise to eddy currents which create a field which resists rotation of said motor, a source of excitation current for said winding joined in curcuit therewith and including a rectifier adapted to be supplied with current from said source of current for said motor, a current relay having a coil contained within said circuit joining said rectifier and the winding of said eddy current torque resisting means and having contacts which are separated when said coil is energized, a generator connected to said motor to be driven thereby, and a power failure relay having a coil connected in circuit with said generator and the contacts of said current relay adapted to be energized when said generator is being driven and the contacts of said current relay are closed, said power failure relay includasoaeor l3 lngcontactswhichlreseparatedwhenthecoil thereof is not energised and adapted on closure to join said generator in circuit with the winding oisaideddycurrenttorqueresbtingmeansand' contacts which are closed when the coil thereof is not energized adapted upon opening to interrupt the circuit joining said rectifier with the winding oi. said eddy current torque resisting means.

9. The combination with an alternating current motor of an eddy-current torque resisting means mounted in driven relationship to the M oi said motor, said eddy-current torque resisting means including windings adapted on excitation to give rise to eddy-currents which create a field which resists rotation said motor, and a source of excitation current for said windings comprising a rectifier and generator driven by the motor the same being alternatively available for use.

10. The combination with an alternating current motor 01' an eddy-current torque resisting means mounted in driven relationship to the shaft of said motor, said eddy-current torque resisting means including windings adapted upon excitation to give rise to eddy-currents which create a field which resists rotation or said motor, and a source 01 excitation current for said windings comprising a rectifier and an accumulator adapted to be charged by said rectifier, said rectiliar and said accumulator being alternatively available for use.

11. The combination comprising a wound rotor alternating current induction motor, adjustable external resistance means having a plurality of adjustment positions connected to and adapted to selectively vary the external resistance 01 the secondary of said motor, eddy-current torque resisting means mechanically connected with the shaft of said motor including windings adapted upon excitation to give rise to eddy-currents which create a field which resists rotation or said motor, excitation current supply means including adjustable current limiting means adapted to supply excitation current to the windings of said eddy-current torque resisting means in selectively variable amount, and control means having a plurality of control positions connected to said adjustable external resbtance of said motor and totheadjustable currentlimitingmeansoisaid excitation currentsupplyadaptedtoeflectapre- 14 determined selection of excitation current for each predetermined selection of. motor external resistance.

12. The combination comprising a wound rotor induction motor; external resistance means having a plurality of adjustment positions connected to and adapted to selectively vary the external resistance 01' the secondary of said motor; power regulating means operative to alter the adjustment position of said external resistance means; eddy-current torque resisting means mechani- 0811:! connected with the shaft or said motor including windings adapted on excitation to give rise to eddy-currents which create a field which resists rotation of said motor; an excitation current supply circuit for the windings of said eddycurrent torque resisting means adapted to be connected to a substantially constant potential source of current supply, including adjustable current limiting means having a plurality of adjustment positions each adapted to supply said windings with a different, substantially constant, predetermined, excitation current; resisting torque regulating means operative to alter the adjustment position of said excitation current supply circuit; and control means shiftable to a plurality of adjustment positions connected to said power regulating means and to said resisting torque regulating means to move the same in coordinated relationship to provide simultaneously for each position of adjustment of said control means, a predetermined position of adjustment of said power regulating means and a predetermined position of adjustment of said excitation current supply circuit, to provide a predetermined selection of excitation current for each predetermined selection of motor external resistance.

FRANK W. WENDELBURG. ERWIN C. BREKELBAUM.

REFERENCES CITED I The following references are of record in the file of this patent.

UNITED STATES PATENTS Number Name Date 2,151,734 Bouton et al. Mar. 28, 1939 2,437,996 Carnegie et al. Mar. 16, 1948 

